1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a semiconductor package capable of suppressing the occurrence of delamination between a semiconductor chip and a mold resin.
2. Description of the Related Art
In recent years, the environment relating to semiconductor devices has been advanced particularly in the field of automotive on-board electronics. The number of electronic parts to be mounted in the engine compartment has been increasing, which has led to demands from the market for guaranteed operation under a high-temperature and high-humidity environment. The methods of testing guaranteed operation are specifically stipulated by public bodies. For example, the moisture sensitivity level (hereinafter referred to as MSL) in J-STD-020D “Moisture/Reflow Sensitivity Classification for Non-hermetic Solid State Surface Mount Devices”, which is a typical standard by IPC/JEDEC, stipulates the storage temperature and humidity conditions, the processing time after opening, and the conditions for the reliability test.
In order to handle such a test, it is necessary to suppress delamination at each adhesion boundary particularly in the semiconductor package. In view of this, various structures and manufacturing methods have hitherto been disclosed.
For example, in Japanese Patent Application Laid-open No. 2005-223305, there is disclosed a resin-encapsulated semiconductor device having improved adhesive properties with a mold resin and a high degree of reliability in which the surface of a lead frame is plated and irregularities are formed on the plated surface formed of Pd/Ni/Au and the like, which is called a PPF (pre-plated frame).
Further, thermal stress produced by differences in the thermal expansion coefficients of the various constituent materials is also a cause of delamination. To suppress this, in Japanese Patent Application Laid-open No. 2001-223304, there is disclosed a resin-encapsulated semiconductor device having a small level of thermal stress in the semiconductor package and a high degree of reliability of the package by adjusting the thermal expansion coefficient and the bending elasticity of the mold resin.
However, semiconductor package delamination cannot be completely suppressed even if those technologies are used. The reason for this is due to differences in the thermal expansion coefficients of the different materials that are used for the lead frame, the mold resin, and the semiconductor chip, respectively, which are the main constituent materials of the semiconductor package. Further, because the surface states are also different due to differences in the processing methods of each material, the internal adhesive strength and stress are in an uneven state. Therefore, even if the adhesive properties of a specific part are improved and the stress of the mold resin is reduced, unless the internal adhesive strength is made relatively more uniform, stress inevitably concentrates at a portion having a weak adhesive strength to induce delamination from that part. Although the adhesive properties between the protective film surface and the encapsulating resin of the semiconductor chip, and the adhesive properties between the lead frame and the encapsulating resin have been improved, there are portions having weak adhesive properties in some places.
FIGS. 4A and 4B illustrate delamination on a side surface of a semiconductor chip. As illustrated in FIG. 4A, a semiconductor chip 2 is mounted on a die pad 3 having a roughened surface 15 on a surface thereof via an adhesive 18 such as a silver paste. A top surface of the semiconductor chip 2 is covered by a protective film 17, which is formed of a polyimide film and the like. The die pad 3 and the semiconductor chip 2 are encapsulated by an encapsulating resin 8. FIG. 4B illustrates an enlarged view of a side surface of the semiconductor chip 2. A peeling portion 19, called the delamination, is present on the side surface of the semiconductor chip 2. The encapsulating resin 8 and the semiconductor chip 2 are not closely adhered, and there is a problem in that humidity resistance is low.